1. Field of the Invention
The present invention relates to a flame retardant polyamide molding resin and to a process for preparing the same. More specifically the present invention relates to a polyamide molding resin having excellent mechanical properties and molding processability as well as flame retarding properties.
2 Description of the Prior Art
Polyamide molding resins are used in a wide range of applications, because of their excellent mechanical strength. However it has been recently required to give them a high level of flame retardancy especially for electric or electronic use, and various kinds of flame retarding agents have been proposed.
Melamine-cyanurate, one of those flame retarding agents for polyamides, is very excellent, so far as the so-called blooming phenomenon is concerned (Japanese Patent Publication Kokai No. 53-31759) That is, melamine cyanurate blended with a polyamide does not bleed out on the surface of the molded article prepared therefrom because of its limited tendency to sublime.
Melamine cyanurate, however, has some disadvantages for use as a flame retarding agent. One disadvantage is the relatively great difficulty in dispersing it in polyamides. A uniform dispersion of the flame retarding agent in the matrix resin is highly desirable for imparting to the resin an excellent flame retarding property. At the same time a non-uniform dispersion of melamine cyanurate downgrades the mechanical properties of the entire molding resin.
Another disadvantage of melamine cyanurate is its high cost in comparison with melamine or cyanuric acid. Melamine cyanurate is usually prepared by reacting an equimolar amount of melamine and cyanuric acid in large amounts of water at a temperature of 80.degree. to 90.degree. C. The precipitate of melamine cyanurate thus obtained should be separated from the water by filtration, dried and crushed to a fine powder. Such a troublesome process naturally results in high cost of the melamine cyanurate.